Foamed hollow profiles are used more particularly as foam insulating pipes and more specifically for the thermal insulation of radiator pipes. For the continuous manufacture of foam insulating pipes a method is known in which a foam base material is applied to a rotating and longitudinally moved core member, whereby the said material can freely foam up towards the outside because in this direction no limit is provided. This has the disadvantage that foam insulating pipes produced in this way have an irregular outer surface and also they have to be covered with an additional enveloping foil when fitted to a radiator pipe. An additional disadvantage is that the wall thickness of the foam pipe is irregular.
An apparatus is also known wherein a fixed outer moulding pipe which is slitted at the top is provided, through whose longitudinal slot via a flat bridge a cylindrical rod is concentrically introduced in such a way that an annular channel is formed, interrupted at the top by the bridge. At either side of the bridge the edges of an inner and outer sheet necessary for pipe manufacture are passed upwardly out of the outer moulding pipe where they are pressed against the bridge by two transfer chains and moved in the longitudinal direction. Prior to the two sheets entering the moulding channel the U-shaped pre-curved outer sheet is supplied with a foam mixture. The foam mixture foams on passage through the annular moulding channel and fills the annular moulding channel on pressing the outer sheet against the inner wall of the outer moulding pipe and pressing the inner sheet against the cylindrical core. On leaving the moulding channel the excess, outwardly projecting sheet edges are cut off and the thus finished pipe strand is cut to length. A particular disadvantage of this manufacturing method is the pronounced friction between the outer sheet and the outer mould, which limits both the length of the apparatus and consequently the manufacturing speed and the number of possible materials which can be used, because high-grade foams produce higher reaction pressures during foaming. However, the upward limit of these reaction pressures is limited because as a result there is a simultaneous and very pronounced increase in friction. A further disadvantage results from the fact that a random construction of the core is not possible. A further disadvantage is that in addition to the outer sheet an inner sheet must be used which must also be provided on its side facing the core with a lubricant in order to keep friction within limits. The inner sheet is merely a manufacturing aid because it is unnecessary for the subsequent use of the foam pipe as an insulating pipe. Furthermore, the inner sheet unnecessarily complicates the manufacturing process and makes the whole installation more fault-prone.
From U.S. Pat. No. 3,585,678 a continuous process is also known wherein once again an outer and an inner sheet are required for the manufacture of a longitudinally slit foam insulating pipe. Both sheets, accompanied by tubular cambering, are introduced into an annular moulding channel, which is radially interrupted at one peripheral point over its length in such a way that the outer sheet engages on the outer wall and the inner sheet on the inner wall formed by the core, whereby shortly before the sheets are introduced into the moulding channel, reactive foam base material is filled into the outer sheet which then completely foams in the moulding channel and is joined to the two sheets. The moulding channel is hereby formed by two outer mould chains and the fixed core secured to a bridge, which is upwardly passed out of the two outer mould chains by an upper parting line. This known process also suffers from the disadvantage of having an additional inner sheet. However, it more particularly suffers from the additional disadvantage that very strong frictional forces occur on the outer wall of the fixed core, so that here again there are limitations with this process regarding the working speed, the cross-section of the articles being produced and the usability of different foam materials.
The same applies regarding another known installation having a fixed mandrel as the inner core, which is secured at the inlet to the installation and projects freely into the fixed or rotary outer mould. Here again an inner sheet is necessary, so that considerable difficulties result from the problems due to friction which cannot be avoided by the use of additional lubricants. Furthermore, it has the additional disadvantage that the mandrel which is only secured on one side does not have an adequate stability to absorb the pressures which occur during foaming without any deflection thereof.
Therefore, due to the above-mentioned problem of mandrel deflection, in the installation known from DAS 2,165,584 the proposal is made to control the deflection by means of a laser beam and to correct the alignment by means of regulating and control members. However, this auxiliary equipment does not lead to a perfect alignment of the fixed inner core and at the same time the whole installation becomes relatively complicated.
Similar problems occur with the installation known from Belgian Pat. No. 670,948, whereby the outer circumference of a cylindrical rod is coated with a polyurethane film. The rod is then passed through a fixed cylindrical outer mould which has a cylindrical shape and configuration. At the same speed as the rod one side of an endless sheet is passed through the fixed mould and which is also cylindrically folded within the cylindrical mould and engages on the outer wall of the latter. To reduce friction the rod and endless sheet are passed through the fixed cylindrical mould at the same speed. Nevertheless the disadvantage still occurs of considerable friction between the endless sheet and the inner wall of the fixed cylindrical mould.
Before the inlet to the fixed cylindrical mould polyurethane is applied to the endless sheet which is folded at this point. The polyurethane then foams completely within the annular space in the fixed cylindrical mould so that the rod leaves the fixed cylindrical mould with a polyurethane foam covering. At this point the endless sheet is folded back into the planar shape and configuration and is returned via guide rollers as an endless band to the inlet of the apparatus.
Apart from the above-mentioned disadvantage of high friction, there is also more particularly the disadvantage that hollow profiles cannot be made because it is only possible to provide a rod with a firmly adhering polyurethane foam covering. There is also no possibility of additionally covering the polyurethane foam with a film, which is, for example, sometimes desired for insulating materials because the foil used comprises an endless, constantly reused conveyor belt.
From U.S. Pat. No. 3,566,448 a process and apparatus for the continuous manufacture of foam profiles, particularly with a polyurethane base is known, which also has the disadvantage that hollow profiles cannot be made which have a substantially closed annular cross-section. In the known apparatus two conveyor belts are juxtaposed, having in each case mould halves which engage against or within one another and form a moulding channel, whose cross-section is semi-cylindrical. If the cross-section of this approximately rod-shaped profile has a somewhat complicated shaping, for example, undercuts, a third conveyor belt can be provided for facilitating the detachment of the conveyor belts from the foam profile.
As the conveyor belts revolve synchronously at the same speed, friction can be kept relatively low. However, this known installation still has the disadvantage of not providing the possibility of manufacturing hollow profiles with an approximately closed annular cross-section, because the profiles have in fact a semi-cylindrical or optionally a rectangular cross-section. It is impossible to make approximately closed cylindrical hollow profiles because only external mould chains are provided, i.e. there is no inner chain. According to a special embodiment, between the two mould halves a core cord with spacers is introduced, but this still does not permit the manfacture of a substantially closed hollow cylindrical profile. Furthermore, it is relatively complicated to remove the core cord from the polyurethane foam profile after the manufacture thereof, because for this purpose the spacers must be separated from the core cord. The further disadvantage exists that the spacers cannot be removed from the polyurethane foam profile but must remain therein. This leads to the disadvantage that at the apparatus inlet the core cord must be continually provided with new spacers. Furthermore, due to the use of the naturally relatively thin core cord, it is not possible to produce a cavity with a relatively large radius. Furthermore, the shaping of the cavity is very imprecise due to the flexibility of the core cord and the incomplete support provided by the spacers. In addition there is no possibility of providing a protective covering on the outer periphery of the insulation which is often desired for insulating pipes.